feat: image paste (Ctrl+V) and drag-and-drop into terminal (#84)

* feat: add image paste and drag-and-drop support

Clipboard paste (Ctrl+V) and drag-and-drop of image files into the
terminal. Images are saved to {workdir}/.claude-images/ and the
absolute path is inserted into the terminal input for Claude to read.

- POST /api/sessions/:id/paste-image endpoint (hand-parsed multipart)
- image-input.js mixin with paste trap technique (works on HTTP)
- Ctrl+V intercepted at xterm keyboard level, routes through hidden
  contenteditable div to capture both image and text clipboard data
- Drag-and-drop on terminal container with visual overlay
- Session cleanup deletes .claude-images/ on destroy

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* security: remove SVG from paste-image allowlist

Drops .svg / image/svg+xml from the paste-image endpoint. SVGs are
served as image/svg+xml via /api/sessions/:id/file-raw, same-origin,
under a CSP that permits inline scripts — which would execute on view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: arkon <arkon.85@hotmail.com>

src/web/public/image-input.js

@@ -0,0 +1,143 @@
+/**
+ * Image Input Mixin - Clipboard paste and drag-and-drop image support
+ *
+ * For paste: intercepts Ctrl+V at the xterm keyboard level, creates a temporary
+ * hidden contenteditable div ("paste trap"), lets the browser's native paste fill
+ * it, then checks for image data. This works on HTTP (no secure context needed).
+ *
+ * For drag-and-drop: listens on the terminal container for file drops.
+ *
+ * @dependency app.js (uses global `app` for sendInput, activeSessionId, showToast)
+ * @dependency panels-ui.js (provides showToast)
+ */
+
+Object.assign(CodemanApp.prototype, {
+
+  initImageInput() {
+    // Drag-and-drop handlers on terminal container
+    const container = document.getElementById('terminalContainer');
+    if (!container) return;
+
+    container.addEventListener('dragover', (e) => {
+      e.preventDefault();
+      if (e.dataTransfer && e.dataTransfer.types.includes('Files')) {
+        container.classList.add('drag-active');
+      }
+    });
+
+    container.addEventListener('dragleave', (e) => {
+      if (!container.contains(e.relatedTarget)) {
+        container.classList.remove('drag-active');
+      }
+    });
+
+    container.addEventListener('drop', (e) => {
+      e.preventDefault();
+      container.classList.remove('drag-active');
+
+      if (!this.activeSessionId) return;
+      if (!e.dataTransfer || !e.dataTransfer.files.length) return;
+
+      const imageFiles = Array.from(e.dataTransfer.files).filter((f) => f.type.startsWith('image/'));
+      if (imageFiles.length === 0) {
+        this.showToast('Only image files are supported', 'error');
+        return;
+      }
+      this._uploadAndInsertImages(imageFiles);
+    });
+  },
+
+  // Called from customKeyEventHandler in terminal-ui.js on Ctrl+V keydown.
+  // Creates a hidden paste trap, lets the browser paste into it, then inspects
+  // the result for images. Works on plain HTTP (no Clipboard API needed).
+  _handleImagePaste() {
+    const self = this;
+
+    // Create a hidden contenteditable div to receive the paste
+    const trap = document.createElement('div');
+    trap.contentEditable = 'true';
+    trap.style.cssText = 'position:fixed;left:-9999px;top:0;width:1px;height:1px;opacity:0;overflow:hidden';
+    document.body.appendChild(trap);
+    trap.focus();
+
+    // Listen for the paste event on our trap
+    trap.addEventListener('paste', function(e) {
+      e.stopPropagation();
+
+      // Check for images in clipboard items
+      var imageFiles = [];
+      var items = e.clipboardData && e.clipboardData.items;
+      if (items) {
+        for (var i = 0; i < items.length; i++) {
+          if (items[i].type.startsWith('image/')) {
+            var blob = items[i].getAsFile();
+            if (blob) imageFiles.push(blob);
+          }
+        }
+      }
+
+      // Clean up the trap
+      setTimeout(function() {
+        if (trap.parentNode) trap.parentNode.removeChild(trap);
+        // Refocus the terminal
+        if (self.terminal) self.terminal.focus();
+      }, 0);
+
+      if (imageFiles.length > 0) {
+        e.preventDefault();
+        self._uploadAndInsertImages(imageFiles);
+      } else {
+        // No image -- extract text and send to terminal
+        var text = e.clipboardData ? e.clipboardData.getData('text/plain') : '';
+        e.preventDefault();
+        if (text) self.sendInput(text);
+      }
+    });
+
+    // Trigger the browser's native paste via execCommand
+    // (this fires the paste event on our focused trap element)
+    document.execCommand('paste');
+  },
+
+  async _uploadAndInsertImages(files) {
+    const sessionId = this.activeSessionId;
+    if (!sessionId) return;
+
+    this.showToast('Uploading ' + files.length + ' image' + (files.length > 1 ? 's' : '') + '...', 'info');
+
+    const paths = [];
+    for (const file of files) {
+      try {
+        const path = await this._uploadPasteImage(sessionId, file);
+        paths.push(path);
+      } catch (err) {
+        this.showToast('Upload failed: ' + (err.message || 'unknown error'), 'error');
+      }
+    }
+
+    if (paths.length > 0) {
+      const pathStr = paths.join(' ');
+      await this.sendInput(pathStr);
+      this.showToast(paths.length + ' image' + (paths.length > 1 ? 's' : '') + ' ready', 'success');
+    }
+  },
+
+  async _uploadPasteImage(sessionId, file) {
+    const form = new FormData();
+    form.append('image', file);
+
+    const resp = await fetch('/api/sessions/' + sessionId + '/paste-image', {
+      method: 'POST',
+      body: form,
+    });
+
+    if (!resp.ok) {
+      const data = await resp.json().catch(() => ({}));
+      throw new Error(data.error || 'HTTP ' + resp.status);
+    }
+
+    const data = await resp.json();
+    return data.path;
+  },
+
+});